Letters 92.29

Though by means of reason he can lead a life which will not bring regrets, yet there resides in this imperfect creature, man, a certain power that makes for badness, because he possesses a mind which is easily moved to perversity. Suppose, however, the badness which is in full view, and has previously been stirred to activity, to be removed; the man is still not a good man, but he is being moulded to goodness. One, however, in whom there is lacking any quality that makes for goodness, is bad.

Seneca, Letters to Lucilius 92.29, translated by Richard Mott Gummere